Much of what is known about their eating habits has come from indirect evidence, such as animal remains found at Neandertal sites and chemical signatures called isotopes detected in their teeth.

The new hard evidence is microfossils of plant material that investigators found in the dental plaque of Neanderthal teeth originally dated to 50,000 years ago, said lead study author Amanda Henry, a graduate student in hominid paleobiology at The George Washington University.

"The formation of dental [plaque] traps the plant microfossils from food particles within the matrix of the plaque deposits, so the microfossils are protected and are a unique record of the plant foods put into the mouth," Henry said.

"So we can say with confidence that this individual Neanderthal ate plants," she added.

Henry discussed her findings at the annual Paleoanthropology Society meeting last month in Vancouver, Canada.

The Shanidar Skeleton

Neanderthals lived in parts of Europe and Asia for more than 200,000 years and disappeared around 30,000 years ago.

They lived in many different environments and survived numerous climatic changes, including some of the coldest and harshest glacial periods, Henry said.

"It seems logical to me that they took advantage of any food sources they had available in their environments, which would vary from place to place and from time to time," she said.

But there had been little hard evidence of variety in their diet, she added.